KLRK1 and neoplasm: When NK cells encounter tumor cells, their activation depends on the balance between activating and inhibitory signals that are produced as the various NK cell receptors interact with their ligands from on target cells.46,58 The main activating receptors include natural cytotoxicity triggering receptors (NCRs; NKp30, NKp44, NKp46), killer cell immunoglobulin-like receptors (KIRs: KIR-2DS and KIR-3DS), and C-type lectin receptors (NKG2D, CD94/NKG2C, NKG2E/H, and NKG2F).